What is your computer system and Firefox? '''https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles''' https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

You need to locate the profiles.ini file and delete this file or use the Profile Manager to create a new profile. See: *https://support.mozilla.org/kb/how-run-firefox-when-profile-missing-inaccessible ---- This issue is caused by a problem with the profiles.ini file or with permissions/ownership of involved folders/files. You can use one of these to make Firefox create a new default profile or recover an existing profile: *Delete the profiles.ini file to make Firefox create a new (default) profile *Use the Profile Manager to create a new profile<br>If you still have an existing profile then click "Choose Folder" in the Profile Manager and browse to the location of a lost profile to recover this profile<br>https://support.mozilla.org/kb/Managing+profiles You should find the profiles.ini file in this hidden location: *Windows: %AppData%\Mozilla\Firefox\<br>*C:\Users\&lt;user&gt;\AppData\Roaming\Mozilla\Firefox\ *Mac: *~/Library/Application Support/Firefox/ *Linux: *~/.mozilla/firefox/ If clearing the profiles.ini file isn't working then also check the location of the cache files. *Windows: *C:\Users\&lt;user&gt;\AppData\Local\Mozilla\Firefox\Profiles\&lt;profile&gt;\ *Mac: *~/Library/Caches/Firefox/Profiles/ *Linux:*~/.cache/mozilla/firefox/ You can also try to rename/delete the Mozilla\Firefox\ folder in both above mentioned locations (main, cache). ---- *http://kb.mozillazine.org/Profile_Manager *https://support.mozilla.org/kb/Managing+profiles *http://kb.mozillazine.org/Profile_folder_-_Firefox